In view of dwindling supplies of traditional diesel fuels, it would be very advantageous if conventional compression-ignition engines, more particularly direct-fuel-injection types, could be easily and inexpensively adapted to burn not only such diesel fuels but also alternative fuels such as 100 percent methanol or ethanol. Such alternative fuels are regarded as attractive substitutes for traditional diesel fuels because methanol can be feasibly sythesized from a wide variety of substances such as coal, natural gas, wood or animal waste. Moreover, ethanol can be feasibly produced by fermentation of starch derived from widely grown plants such as sugar cane or corn. Furthermore, the amounts of nitrogen oxides and smoke-associated particulates are inherently lower and practically nonexistent, respectively, when burning such alcohol fuels as compared to burning traditional diesel fuels.
However, these alternative fuels are characterized by a cetane number or ignition value on the order of about 0-10 whereas traditional diesel fuels, such as Grade 2-D diesel fuel, are characterized by a cetane number of at least 40. Consequently, unlike traditional diesel fuels, these relatively lower-cetane-number alternative fuels do not readily autoignite under normal compression ratios and temperatures of about 538.degree. C. (1000.degree. F.), in an open combustion chamber of a compression-ignition engine, merely by contacting and mixing with intake air which has been compressed and thereby heated by a piston.
Such relatively lower-cetane-number alternative fuels can be locally ignited with the aid of an electrically-energized glow plug or spark plug which directly heats a nearby air/fuel mixture to a sufficiently elevated temperature of about 1000.degree. C. (1832.degree. F.). However, another major problem exists of completely igniting and burning all of the alternative fuel that is directly injected into the open combustion chamber. This problem is due to the way fuel has been typically directly injected into the open combustion chamber of a modern compression-ignition engine.
As shown in U.S. Pat. No. 4,275,844 issued to Grgurich et al. on June 30, 1981, a conventional open combustion chamber of a direct-injection compression-ignition engine typically includes a relatively-high-pressure fuel injector having a plurality of very small fuel spray orifices. These orifices periodically and simultaneously spray a plurality of distinct and evenly spaced high pressure fuel streams towards various peripheral portions of the open combustion chamber which is already filled with fresh intake air. This pattern of relatively concentrated conical fuel streams separated by sectors of fuel-deficient intake air, similar to the radial spokes of a wheel, is desirable for modern direct-injection engines to provide each fuel stream without enough kinetic energy so that it can quickly and adequately penetrate, atomize, mix, and combust with the required larger amounts of intake air before each cyclic power stroke of the open combustion chamber has substantially begun.
If a glow plug or spark plug is electrically-energized to produce a localized elevated temperature of about 1000.degree. C. (1832.degree. F.) and is positioned in close enough proximity to one of the mutually-spaced fuel streams of relatively lower-cetane-number alternative fuel, usually only that one fuel stream and other sufficiently close fuel streams will ignite. However, the fuel-deficient sectors of air separating each of the other remotely spaced fuel streams will prevent the flame from propagating to those other fuel streams. Consequently, the fuel streams which are not ignited, or are only partially burned, are exhausted from the open combustion chamber as either wasted raw fuel or imcompletely combusted fuel. This, of course, signficantly and undesirably reduces the fuel economy and power output of the engine and raises the level of noxious emissions, particularly hydrocarbons, exhausted from the open combustion chamber. Only at high engine loads is the combustion system less dependent on flame propagation for complete ignition because, under such conditions, the initial pressure rise and associated temperature rise may be sufficiently high to force autoignition of the remote fuel streams.
In U.S. Pat. No. 3,244,159 issued to Meurer on Apr. 5, 1966, there is disclosed a fuel combustion system fashioned in such a way that an intensive swirling or unidirectional gas flow results in the combustion chamber during engine operation. A localized flame of burning fuel is started on a fuel stream injected adjacent to an igniting element and the flame and air/fuel mixture is moved along by that intensive swirling gas flow so that the flame contacts and ignites other injected fuel streams. However, the complete dependence upon swirling gas flow to achieve propagation of a flame through a non-autoignitable fuel carries the penalty of lower fuel economy due to increase heat rejection (i.e., the swirling gas flow disrupts the insulating gas boundary layer on the combustion chamber walls). Moreover, modifications, for example, to the air intake port(s) or to the air intake valve(s) for inducing intensive swirling gas flow also undesirably create gas flow restrictions which increase pumping losses of the engine and thereby further lower fuel economy.
In U.S. Pat. No. 4,548,172 issued to Bailey on Oct. 22, 1985, there is shown a fuel combustion system including a multiple-orifice fuel injector, a fuel ignition-initiating means, a secondary fuel spray orifice, and an impingement surface element having a deflecting face spaced from and facing that secondary orifice. During engine operation, this arrangement effectively generates an auxiliary cloud of atomized fuel which interconnectedly bridges other mutually-spaced fuel streams so a flame can be rapidly propagated without depending on the existence of swirling gas flow. However, at above about one quarter to one half engine loads, such an arrangement may produce excessive smoke when burning non-oxygenated fuels such as diesel fuel or unleaded gasoline, respectively. That is because the size of the secondary orifice is usually chosen in accordance with ensuring satisfactory engine operation at light engine loads and therefor the size of the secondary orifice may be somewhat too large for spraying non-oxygenated fuels when the engine is operated at heavy loads. Consequently, at heavy engine loads, too much non-oxygenated fuel may be sprayed through the secondary orifice such that the fuel is unable to adequately mix and combust with air. Furthermore, the above arrangement may require special modifications to standard off-the-shelf fuel injectors and/or pistons which add to the cost of the engine.
The present invention is directed to overcoming one or more of the problems as set forth above.